[tip: x86/mm] x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default

[tip: x86/mm] x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default

[tip-bot2 for Kirill A. Shutemov]

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     81256a50aa0fddefbf4849db8cad9f70c5167c04
Gitweb:        https://git.kernel.org/tip/81256a50aa0fddefbf4849db8cad9f70c5167c04
Author:        Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
AuthorDate:    Mon, 17 Feb 2025 18:38:21 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 21 Feb 2025 15:05:45 +01:00

x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default

Currently memremap(MEMREMAP_WB) can produce decrypted/shared mapping:

  memremap(MEMREMAP_WB)
    arch_memremap_wb()
      ioremap_cache()
        __ioremap_caller(.encrytped = false)

In such cases, the IORES_MAP_ENCRYPTED flag on the memory will determine
if the resulting mapping is encrypted or decrypted.

Creating a decrypted mapping without explicit request from the caller is
risky:

  - It can inadvertently expose the guest's data and compromise the
    guest.

  - Accessing private memory via shared/decrypted mapping on TDX will
    either trigger implicit conversion to shared or #VE (depending on
    VMM implementation).

    Implicit conversion is destructive: subsequent access to the same
    memory via private mapping will trigger a hard-to-debug #VE crash.

The kernel already provides a way to request decrypted mapping
explicitly via the MEMREMAP_DEC flag.

Modify memremap(MEMREMAP_WB) to produce encrypted/private mapping by
default unless MEMREMAP_DEC is specified or if the kernel runs on
a machine with SME enabled.

It fixes the crash due to #VE on kexec in TDX guests if CONFIG_EISA is
enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20250217163822.343400-3-kirill.shutemov@linux.intel.com
---
 arch/x86/include/asm/io.h | 3 +++
 arch/x86/mm/ioremap.c     | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index ed580c7..1a0dc2b 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -175,6 +175,9 @@ extern void __iomem *ioremap_prot(resource_size_t offset, unsigned long size, un
 extern void __iomem *ioremap_encrypted(resource_size_t phys_addr, unsigned long size);
 #define ioremap_encrypted ioremap_encrypted
 
+void *arch_memremap_wb(phys_addr_t phys_addr, size_t size, unsigned long flags);
+#define arch_memremap_wb arch_memremap_wb
+
 /**
  * ioremap     -   map bus memory into CPU space
  * @offset:    bus address of the memory
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 38ff779..42c90b4 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -503,6 +503,14 @@ void iounmap(volatile void __iomem *addr)
 }
 EXPORT_SYMBOL(iounmap);
 
+void *arch_memremap_wb(phys_addr_t phys_addr, size_t size, unsigned long flags)
+{
+	if ((flags & MEMREMAP_DEC) || cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
+		return (void __force *)ioremap_cache(phys_addr, size);
+
+	return (void __force *)ioremap_encrypted(phys_addr, size);
+}
+
 /*
  * Convert a physical pointer to a virtual kernel pointer for /dev/mem
  * access